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Dotted notation parser with pattern matching

Project description


Sometimes you want to fetch data from a deeply nested data structure. Dotted notation helps you do that.

Let's say you have a dictionary containing a dictionary containing a list and you wish to fetch the ith value from that nested list.

>>> import dotted
>>> d = {'hi': {'there': [1, 2, 3]}}
>>> dotted.get(d, 'hi.there[1]')


Probably the easiest thing to do is pydoc the api layer.

$ pydoc dotted.api


See grammar discussion below about things you can do get data via dotted.

>>> import dotted
>>> dotted.get({'a': {'b': {'c': {'d': 'nested'}}}}, 'a.b.c.d')


Update will mutate the object if it can. It always returns the changed object though. If it's not mutable, then get via the return.

>>> import dotted
>>> l = []
>>> t = ()
>>> dotted.update(l, '[0]', 'hello')
>>> l
>>> dotted.update(t, '[0]', 'hello')
>>> t

Update via pattern

You can update all fields that match pattern given by either a wildcard OR regex.

>>> import dotted
>>> d = {'a': 'hello', 'b': {'bye'}}
>>> dotted.update(d, '*', 'me')
{'a': 'me', 'b': 'me'}


You can remove a field or do so only if it matches value. For example,

>>> import dotted
>>> d = {'a': 'hello', 'b': 'bye'}
>>> dotted.remove(d, 'b')
{'a': 'hello'}
>>> dotted.remove(d, 'a', 'bye')
{'a': 'hello'}

Remove via pattern

Similar to update, all patterns that match will be removed. If you provide a value as well, only the matched patterns that also match the value will be removed.


Use to match a dotted-style pattern to a field. Partial matching is on by default. You can match via wildcard OR via regex. Here's a regex example:

>>> import dotted
>>> dotted.match('/a.+/', 'abced.b')
>>> dotted.match('/a.+/', 'abced.b', partial=False)

With the groups=True parameter, you'll see how it was matched:

>>> import dotted
>>> match('hello.*', 'hello.there.bye', groups=True)
('hello.there.bye', ('hello', 'there.bye'))

In the above example, hello matched to hello and * matched to there.bye (partial matching is enabled by default).


You may with to expand all fields that match a pattern in an object.

>>> import dotted
>>> d = {'hello': {'there': [1, 2, 3]}, 'bye': 7}
>>> dotted.expand(d, '*')
('hello', 'bye')
>>> dotted.expand(d, '*.*')
>>> dptted.expand(d, '*.*[*]')
('hello.there[0]', 'hello.there[1]', 'hello.there[2]')
>>> dotted.expand(d, '*.*[1:]')


Dotted notation looks similar to python. Both dot fields and bracketed fields use keys() and __getitem__() internally. A dot field expects to see a dictionary-like object. A slot field is biased towards sequences (like lists, tuples, and strs) but can act on dicts as well. Dotted also supports slicing notation as well as transforms discussed below.

Key fields

A key field is expressed as a or part of a dotted expression, such as a.b. The grammar parser is pretty permissive for what can be in a key field. Pretty much any non-reserved char will match. Note that key fields will only work on objects that have a keys() method. Basically, they work with dictionary or dictionary-like objects

>>> import dotted
>>> dotted.get({'a': {'b': 'hello'}}, 'a.b')

If the key field starts with a space or -, you should either quote it OR you may use a \ as the first char.

Bracketed fields

You may also use bracket notation, such as a[0] which does a __getitem__ at key 0. The parser prefers numeric types over string types (if you wish to look up a non-numeric field using brackets be sure to quote it). Bracketed fields will work with pretty much any object that can be looked up via __getitem__.

>>> import dotted
>>> dotted.get({'a': ['first', 'second', 'third']}, 'a[0]')
>>> dotted.get({'a': {'b': 'hello'}}, 'a["b"]')

Numeric types

The parser will attempt to interpret a field numerically if it can, such as field.1 will interpret the 1 part numerically.

>>> import dotted
>>> dotted.get({'7': 'me', 7: 'you'}, '7')


Sometimes you need to quote a field which you can do by just putting the field in quotes.

>>> import dotted
>>> dotted.get({'has . in it': 7}, '"has . in it"')

The numericize # operator

Non-integer numeric fields may be interpreted incorrectly if they have decimal point. To solve, use the numerize operator # at the front of a quoted field, such as #'123.45'. This will coerce to a numeric type (e.g. float).

>>> import dotted
>>> d = {'a': {1.2: 'hello', 1: {2: 'fooled you'}}}
>>> dotted.get(d, 'a.1.2')
'fooled you'
>>> dotted.get(d, 'a.#"1.2"')


Dotted slicing works like python slicing and all that entails.

>>> import dotted
>>> d = {'hi': {'there': [1, 2, 3]}, 'bye': {'there': [4, 5, 6]}}
>>> dotted.get(d, 'hi.there[::2]')
[1, 3]
>>> dotted.get(d, '*.there[1:]')
([2, 3], [5, 6])

The append + operator

Both bracketed fileds and slices support the '+' operator which refers to the end of sequence. You may append an item or slice to the end a sequence.

>>> import dotted
>>> d = {'hi': {'there': [1, 2, 3]}, 'bye': {'there': [4, 5, 6]}}
>>> dotted.update(d, '*.there[+]', 8)
{'hi': {'there': [1, 2, 3, 8]}, 'bye': {'there': [4, 5, 6, 8]}}
>>> dotted.update(d, '*.there[+:]', [999])
{'hi': {'there': [1, 2, 3, 8, 999]}, 'bye': {'there': [4, 5, 6, 8, 999]}}

The append-unique +? operator

If you want to update only unique items to a list, you can use the ? postfix. This will ensure that it's only added once (see match-first below).

>>> import dotted
>>> items = [1, 2]
>>> dotted.update(items, '[+?]', 3)
[1, 2, 3]
>>> dotted.update(items, '[+?]', 3)
[1, 2, 3]

The invert - operator

You can invert the meaning of the notation by prefixing a -. For example, to remove an item using update:

>>> import dotted
>>> d = {'a': 'hello', 'b': 'bye'}
>>> dotted.update(d, '-b', dotted.ANY)
{'a': 'hello'}
>>> dotted.remove(d, '-b', 'bye again')
{'a': 'hello', 'b': 'bye again'}


You can use dotted for pattern matching. You can match to wildcards or regular expressions. You'll note that patterns always return a tuple of matches.

>>> import dotted
>>> d = {'hi': {'there': [1, 2, 3]}, 'bye': {'there': [4, 5, 6]}}
>>> dotted.get(d, '*.there[2]')
(3, 6)
>>> dotted.get(d, '/h.*/.*')
([1, 2, 3],)

Dotted will return all values that match the pattern(s).

The match-first operatoer

You can also postfix the wildcard or regex with a ?. This will return only the first match.

>>> import dotted
>>> d = {'hi': {'there': [1, 2, 3]}, 'bye': {'there': [4, 5, 6]}}
>>> dotted.get(d, '*?.there[2]')


You can optionally add transforms to the end of dotted notation. These will be applied on get and update. Transforms are separated by the | operator and multiple may be chained together. Transforms may be parameterized using the : operator.

>>> import dotted
>>> d = [1, '2', 3]
>>> dotted.get(d, '[1]')
>>> dotted.get(d, '[1]|int')
>>> dotted.get(d, '[0]|str:number=%d')

You may register new transforms via either register or the @transform decorator. Look at for preregistered.

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